The changing of brake pads on a disc brake caliper assembly is generally accomplished through the use of a C-clamp. Mechanics find the use of such a C-clamp to be somewhat difficult because of the lack of control associated with it. Such a clamp tends to wander from the center of the piston and could cause damage to the cylinder if excessive pressure is applied. Thus, the continuing wandering or walking of the C-clamp while trying to depress the piston into the cylinder requires many resettings to perform the otherwise simple operation of depressing the piston to its retracted position within a piston cylinder. In other words, much time and potential damage is associated with the present state of the art.
Conventionally, the pistons of the disc brake assemblies have a closed end adjacent the closed end of the cylindrical bore and an open end adjacent the end operating in conjunction with the disc brake pad. The piston is axially moved outwardly by hydraulic fluid to push a brake shoe having a brake lining against the disc of a brake disposed between the outer end of the piston and the support bracket of the disc brake caliper housing.
It is well known that these pistons tend to stick because of dirt and/or corrosion being formed or disposed between the piston and the inside wall of the cylinder bore. As the brake pads wear, the pistons project outwardly from the cylinder bore. Because the piston is hollow and axially short as compared to its diameter, it is difficult to move the piston into the bore of the caliper housing either by hand or through the use of the C-clamp. That is, it tilts or cocks easily about its axis to bind within the cylindrical bore.
It is known to provide a piston puller which fits inside the open end of the piston and thereby enables the piston to be moved into or out of the cylindrical bore. Such devices are disclosed in the U.S. Pat. Nos. 3,786,551 and 4,009,515. In each of these instances, however, the device requires a particular type of gripping member which must be placed inside the hollow piston and thereafter activated through a rotation of a part causing the gripping member to expand and thus come into contact with the inside surface of the cup. Once this is done, the piston cup may then be moved into or out of the cylinder bore. In each of these prior art mechanisms the threaded shaft is maintained in a nonrotating condition while nuts or tightening members are turned to effect the desired inward or outward motion of the piston with respect to the cylinder bore.